1. Field of the Invention
This invention relates generally to cellular network communications; and more particularly to the wireless link between a base station and a mobile station.
2. Background of the Invention
The general structure and operation of cellular wireless communication systems is generally known. A cellular network infrastructure typically includes a plurality of base stations that each service wireless communications for one or more cellular mobile stations within a respective cell. Typically, each base station supports a plurality of sectors within its serviced cell. Base Station Controllers (BSCs) typically service a plurality of base stations and coordinate operations within the cells serviced by the base stations. A mobile switching center (MSC) services a plurality of base station controllers and couples to the Public Switched Telephone Network (PSTN). Typically, the base station controllers or the MSC couple to the Internet to service packetized communications there through.
Cellular wireless infrastructures typically support one or more wireless protocol standards. These wireless protocol standards include Code Division Multiple Access (CDMA) protocol standards such as IS-95A, IS-95B, 1X-RTT, 1xEV-DO, 1xEV-DV, UMTS, and other CDMA type protocols. Alternately, the wireless protocol standard may service a Time Division Multiple Access (TDMA) standard such as the GSM standard, the North American TDMA standard, or other TDMA standards. The cellular mobile stations operating in the service area communicate with the base stations using such supported wireless protocol standards.
As is known, transmissions from a base station to a cellular mobile station thereof are called forward link transmissions. Likewise, transmissions from cellular mobile stations to base stations are called reverse link transmissions. The cellular network infrastructure coordinates and manages both the forward link and reverse link transmissions. Due to mobility of the cellular mobile stations, the power of forward link transmit power and reverse link transmit power are controlled. In CDMA systems, for example, reverse link transmit power and forward link transmit power must be closely controlled for each cellular mobile station. Existing CDMA wireless protocol standards provide strict guidelines for closed loop power control. With these standardized operations, a servicing base station controls reverse link transmit power by sending (as necessary) power control bits on the forward link to each serviced cellular mobile station. These power control bits are typically contained in the power control sub-channel. For each power control bit, the cellular mobile station either increases its reverse link transmit power or decreases its reverse link transmit power, depending upon the value of the power control bit.
Unfortunately, prior cellular systems were predisposed to lose the reverse link. In order to reduce interference within a service sector or cell, a prior art servicing base station directed its service cellular mobile stations to transmit at a minimum acceptable reverse link transmit power level via use of the power control bits accordingly. Thus, reverse link transmissions typically arrived with minimally sufficient power at the servicing base station. With prior systems, when the reverse link was lost, the base station (or servicing BSC) typically considered the call as lost and either kept forward link transmissions at a constant level or reduced power of the forward link transmissions. Thus, many calls were dropped due to these prior power control operations.
Problems with prior power control operations were caused by errors on the power control sub-channel, a power-up bit transmitted by the base station may be incorrectly demodulated by the mobile station as a power-down bit. These “presumed” power-down bits caused a receiving cellular mobile station to reduce its reverse link transmit power when it should have increased its reverse link transmit power. When a cellular mobile station was in soft handoff between base stations or softer handoff between sectors of the base station in a CDMA system, the cellular mobile station would receive multiple power control bits from the multiple currently serving sectors. However, the cellular mobile station was disposed to more strongly consider a power-down power control bit than power-up power control bit. Thus, the cellular mobile station in such case was predisposed to reduce its reverse link transmit power which resulted frequently in loss of the reverse link. Thus, in many prior operations, calls were dropped because of the failure to properly control reverse link transmit power of the cellular mobile station.
Thus, a need exists for improved reverse link power control operations within a cellular network.